1. Field of the Invention
The present invention is directed to a non-linear load driving technique and more particularly to a light emitting diode (LED) driving circuit.
2. Description of Related Art
A light emitting diode (LED) has advantages of a small size, a high light emitting efficiency, a long lifespan, a fast response speed, a good color rendering index (CRI) and so on and thus, is widely used. Comparing with a fluorescent tube using mercury, the LED is more environmentally friendly. Thus, in order for power-saving and pollution-free illumination, the LED gradually takes the place of the fluorescent tube.
As for an LED driving circuit using an AC voltage source, a bridge rectifier circuit is commonly adopted to obtain a DC voltage and a large capacitor is used to filter the DC voltage to obtain a stable DC-link voltage served as an input of a high-frequency DC-to-DC switching converter. Generally, such type of LED driving circuit would cause input current distortion. As a result, a great amount of harmonic waves are generated and power factors are low. In order to avoid wave distortion of an AC input current, a power factor corrector (PFC) is typically additionally added to a previous stage of the DC-to-DC converter to form a dual-stage driving structure. Meanwhile, the entire power factors of the LED driving circuit are also enhanced by the function of the PFC. However, such type of LED driving circuit requires more active switches and often results in greater switching losses in a hard switching control mode during periods of switching the active switches.
Under the existing technology, a designer may mitigate the switching losses of the active switches by utilizing a soft-switching control mode. For instance, a commonly used soft-switching control mode may be as two types, zero-voltage switching-on (ZVS) and zero-current switching-on (ZCS). Neither the ZVS nor the ZCS control mode would substantially lead the active switches to power losses during the switching periods.
However, in order to implement the soft-switching control mechanism, it is common to additionally add auxiliary circuits or snubber circuits in the LED driving circuit, while those additional circuits would result in design complexity and cost of the LED driving circuit being increased.